1. Field of the Invention
The invention relates to an apparatus for developing photographic emulsion. In the apparatus of the invention a web coated with a photographic emulsion or other photosensitive material forms one wall of a processing chamber and processing chemicals are introduced sequentially into the stationary chamber. The heating of the processing chemicals to their required temperatures is accomplished by applying microwave energy to the chemicals upstream of the chamber.
2. Background Art
The commercial production of photographic film involves the preparation of very large batches, on the order of 1500 L, of chemically complex photographic emulsions whose batch-to-batch variation in photographic response be kept to a minimum. The photographic characteristics of an emulsion (contrast, speed, reciprocity, maximum density and fog) are commonly referred to as its sensitometric properties. Currently sensitometric properties are assayed on each batch of emulsion by actually running a portion of the emulsion through the commercial scale coating machinery, to provide a section of coated web, exposing the emulsion in a controlled fashion in a sensitometer, developing the image by conventional processing bath technology, and measuring the image in a densitometer. The developing of the image in conventional processing baths is very time-consuming, wastes large amounts of materials, and is almost completely inflexible to changing parameters.
An apparatus wherein a section of film could be developed in a small space with complete flexibility as to time, temperature and processing chemicals would obviate all of the problems of the earlier method. To provide such an apparatus one needs a developing chamber of small working volume and one needs to be able to control its temperature quickly and precisely. The art provides several examples of small working volume chambers for developing film.
U.S. Pat. No. 3,149,550 (Lohse et al.) discloses an apparatus for developing film wherein there is provided a minute processing chamber defined by the emulsion side of an exposed photographic film and a platen closely spaced in parallel relationship thereto. The spacing between the platen and film is preferably sufficiently close so that the processing liquids introduced therebetween are held within the chamber by capillary force. Successively small amounts of processing fluids are passed to the processing chamber, with each succeeding fluid serving to supplant the preceding fluid in the chamber. Means are provided for delivering processing fluid to the processing chamber through opening in the platen. The distance between the plane of the platen surface and the plane of the film engaging surface of the frame is in the preferred embodiment from about 0.01 to 0.030 inch. The apparatus is preferably provided with a heater block supporting the platen and carrying a fluid passage which is in communication with the central opening of the platen. The heater block may or may not be integral with the platen. A heating element preferably is embedded within the heater block. The fluid supply passageways within the heater block are of a sufficient length to preheat the processing fluids.
U.S. Pat. No. 3,744,394 (Firth) discloses an apparatus for processing film wherein a latent image on a sheet or strip of film is processed to produce a dry, developed film by positioning it between a pair of spaced platens. The one platen is moved into contact with the film and then the other platen is moved into position so as to clamp the film therebetween. The other platen is also provided with a resilient frame member which provides a seal with respect to the support side of the film. A recess in the one platen is interconnected to the processing solutions through a metering valve so that each solution is moved into the recess in a required order so as to develop the latent image area. Each platen is provided with a cavity in which a foil heating element is arranged in contact with the cavity surface. With this arrangement, the flow of solution is maintained at a generally consistent and uniform temperature from the point of introduction into the recess to the point at which it is withdrawn after processing has been completed.
U.S. Pat. No. 3,886,576 (Stoffel) discloses an apparatus for developing a film insert on an aperture card. The apparatus comprises a sealing member on a receptacle arranged to contact a portion of the card bordering the aperture to form a processing chamber that confines processing solutions to an area on the card including all the film insert overlying the aperture, and means for compressing the card against the sealing member to render the compressed portion of the card substantially impervious to processing solution. The apparatus further includes means for supplying processing solutions to a processing chamber including all the film member overlying the aperture. The patent does not describe heating means, but observes "Because of film processing considerations which are well known in the art, it may be necessary to provide the developer and fixer tanks with a solution heater assembly (not shown) for maintaining these fluids at a predetermined temperature."
U.S. Pat. No. 3,936,854 (Smith) discloses an apparatus for developing photosensitive material. The apparatus comprises two members between which the material is clamped during the development process. The first member which is fixed, has an open-end chamber that is interconnected to two sources of air under pressure and to a reservoir for at least once processing fluid. This chamber is also provided with two concentrically arranged sealing means for retaining the processing fluid in proper relation to the image area being developed when the material is clamped between the two members. The second member is movable relative to the first member for clamping the material therebetween via the sealing means. The second member is provided with a recess in which a heater member and a transparent plate are mounted and each of which engages the facing surface of the support. The heater member is provided with a duct through which hot air can be circulated or in which a heating element or coil can be arranged. The heat transferred to the member is conducted to the support by the portion in contact therewith and also to the transparent plate, the surface of which also engages the surface of the support.
U.S. Pat. No. 4,884,093 (Bohmig) discloses an apparatus for developing a film sheet of a film punched card. The apparatus comprises a developing chamber limited on one side by the emulsion coating of the film and on the other by a chamber which is formed from a metal block having a heating cartridge embedded in it. Temperature is maintained accurately and invariably.
There is one disclosure of a heating system that provides a fast, dynamic response. European published application 417782 (Gebo) discloses a control system for a process variable. An example is given utilizing the control system to regulate a microwave generator to provide precise heating of a flowing fluid. The reference states that the control system may be utilized in a process for coating photographic paper or film.
The art provides apparatus for repetitive developing processes under constant conditions. The cited examples are adapted for a developing operation performed on a strip of material that is moved intermittently. The use of a microwave heat source in combination with a developing chamber to provide a developing apparatus that is small and versatile is not disclosed or suggested.
The film developing art addresses the need for providing processing chemicals at an elevated temperature by (1) heating the processing chamber (Lohse, Firth, Smith and Bohmig) or (2) heating the processing chemicals before they enter the chamber (Lohse and Stoffel). When the chamber is complex or involves a large mass of metal, a system that heats the chamber is slow to respond to a requirement for different temperatures. It is therefore suited to repetitive processes under constant conditions; it is unsuited to procedures such as test paradigms, where temperatures must be frequently changed. Heating the processing chemicals apart from the processing chamber allows one to change temperatures--provided that the chamber and connecting plumbing incorporate minimal amounts of thermally conductive material--but the means for heating disclosed in the film processing art, namely heating blocks and heating baths, require separate blocks or baths for each combination of chemical and temperature. An apparatus to be used for testing various emulsions that require different development temperatures would be impractically large. Moreover, the use of baths leads to degradation of chemicals that are maintained at elevated temperatures.
There thus exists a need for a compact developing apparatus that can quickly modify processing chemistries, particularly with respect to temperature.